777E and 777F Off-Highway Truck Power Train Caterpillar

Illustration 1	g01247522
Location of the Modulating Valves (Transmission Clutch) (1) Number 1 clutch modulating valve (2) Number 2 clutch modulating valve (3) Number 3 clutch modulating valve (4) Number 4 clutch modulating valve (5) Number 5 clutch modulating valve (6) Number 6 clutch modulating valve (7) Number 7 clutch modulating valve (8) Round connector (through transmission case) (9) Rectangular connector to the chassis harness

Illustration 2	g01247671
Modulating Valve (Transmission Clutch)

The transmission clutch solenoid modulating valves are mounted on the top of the transmission. There is one modulating valve for each of the seven transmission clutches.

The modulating valves are outputs of the Chassis Electronic Control Module (ECM). The transmission clutch solenoid modulating valves are proportional solenoid valves. The modulating valves are used by the Chassis (ECM) to directly modulate the oil pressure that is sent to each individual clutch. When the operator selects a direction or when the operator selects a speed the power train ECM sends a pulse width modulated signal (PWM) in order to vary the current to the clutch solenoid. The distance that is travelled by the solenoid plunger (valve) is proportional to the electrical current of the solenoid. The position of the solenoid plunger (valve) controls the oil pressure of the selected clutch. The amount of current that is sent to the modulating valve regulates the amount of oil pressure that is supplied to the selected clutch. When the Chassis (ECM) sends the maximum current to the modulating valve, the oil pressure in the clutch is at the maximum. When no current is sent to the modulating valve, the oil pressure in the clutch is at the minimum.

The Chassis (ECM) will activate the modulating valves that are selected by the operator. Modulating valves supply oil to the clutches. Modulating valves (2) , (3) , (4) , (5) , (6) , and (7) supply oil to the corresponding clutch. In order for the machine to move, two clutch solenoids must be energized. When the transmission is in neutral, only one modulating valve (3) is energized.

The modulating valves have a connector with two contacts. One contact receives power from the corresponding connector contacts of the Chassis (ECM). The wiring harnesses have two connectors. Connector (8) passes through the transmission case to connector (9) . Connector (9) interfaces with the vehicle harness.

Note: The solenoid coils are not designed to be operated at 24 DCV directly. The power train ECM sends a 24 volt PWM signal at a duty cycle which provides an average voltage of about 12 volts to the solenoid coils. Do not energize the solenoid coils with 24 DCV (+battery). The life of the solenoid coils will be drastically reduced if the solenoid coils are energized with 24 DCV (+battery). If the solenoid coils must be energized by a source that is different from the power train ECM, use 12 DCV to energize the solenoid coils.

ReferenceFor information on troubleshooting the transmission, refer to the Service Manual module for Testing and Adjusting, "Power Train Troubleshooting" for the machine that is being serviced.

ReferenceFor information on calibrating the modulating valves, refer to the Service Manual module for Testing and Adjusting, "Calibration and Programming" for the machine that is being serviced.

ReferenceFor information on calibrating the modulating valves, refer to the Service Manual module for Testing and Adjusting, "Fill Time for the Transmission Clutch - Calibrate" for the machine that is being serviced.

ReferenceFor more information on the Chassis Electronic Control Module (ECM), refer to the Service Manual module for Systems Operation, "Electronic Control Module (Power Train)" for the machine that is being serviced.